Variable speed motor control



Dec. 15, 1936. B. A. WITTKUHNS El AL 2,064,454

VARIABLE SPEED MOTOR CONTROL Filed June 1550, 1931 3 Sheets-Sheet l f \6a '1 I J V W Higii'i INVENTORS 52505010 /1. M r/mva.

Dec. 15, 1936. a. A. wrrrKuHNs ET AL 2,064,454

' VARIABLE SPEED MOTOR CONTROL Fi'led June so; 1931 s Sheets-Sheet 2 UFOLLOWUP ELEMENT v Zzg. Z1.

ON QENSITIVE EIMEN DRIVES RILLDW-UP ELEMENT nw L INVENTORS BRu/vofl.W/rr/ruHA/a% =E fkmm/c NWMK/NS BY 0 o W1! SQGNAL ATTORNEY.

Dec..l5, 1936. WITTKUHNS 2,064,454

VARIABLE SPEED MOTOR CONTROL Filed June 30, 1931 3 Sheets-Sheet 3INVENTORS v BRUNO flJA/mnuHNsi fimmm M.WH7'/f/N6' BY 1 Minimum.

Patented Dec. 1936 UNITED STATES PATENT. OFFICE 2,064,454 VARIABLEarm-1n Moron CONTROL Application June so, 1931, Serial No. 547,872

16 Claims.

This invention relates to motor control by means of grid controlled gasor vapor filled rectifier tubes. These tubes are also known as .hotcathode grid controlled rectifiers or simply as grid glow tubes.

of these tubes seems to be more or less like those of three-elementthermionic tubes, there is a. decided difference in their control.Inasmuch as special means have to be provided to interrupt the D. C.plate current, which? otherwise, after the tube has once started, wouldno longer be subject to the control of the grid, it is in most casesadvisable to use A. C. for the plate supply, or, if D. C. is used,provide means to interrupt this D. C. if the tube has to be stopped. Thegreat advantage of these tubes, however, is the possibility ofcontrolling comparatively large amounts of power by means of very smallinput energies. excellently suited for use as relays, with the addedadvantage of no moving parts whatsoever.

In the present invention, these tubes are used' to control power drivenmotors, especially in such cases where the motors not only-have to bestopped and started but where they also have to to theme of such motorsin all kinds of apparatus where the controlling element is not able tosupply appreciable amounts of either mechanical or electrical energy,as, for instance, in follow-up arrangements for sensitive devices suchas gyro compasses, magnetic compasses, and for remote control systems,and the like.

In the accompanying drawings,

Fig. 1 shows by a wiring diagram the general scheme of a rectifiercontrolled reversing motor.

Fig. 2 shows a modification of the same circuit for higher sensitivityand accuracy.

Fig. 3 shows another modification of the same circuit as applied to afollow-up system.

Fig. 4 shows a, simplified modification of the circuit in Fig. 3.

Fig. 5 shows another circuit for the same general purpose in which thecontrol of the rectifier tubes is different.

Referring to Fig. 1, l and 2 are two grid glow tubes constituting whatmay be termed a grid glow or rectifier tube unit, in which the usualplate, grid and filament are shown in the conventional manner. Nofilament heating supply is shown in this circuit for the sake ofsimplicity. A transformer 3 is provided to supply the necessary voltagesto the whole apparatus. The primary 4 of the transformer is connected toan alternating current line 5 and B. The high Whilethe generalappearance They, therefore, are

be .reversed. Furthermore, this invention relates 1 tension secondary Iof this transformer has a center tap 8. Between the end 9 ofthis'winding and the center tap 3 exists a potential which is used forthe plate supply of the rectifiers I and 2. Point 8 is connected to theconnection In 5 of the filaments of the tubes, while from point 9 thecircuit goes through the armature l l of a power motor and through thefield coils l2 and current passing through tube 2 will pass througharmature II and field coil l3 of the motor. The- 5 field coils arearranged in such a way that the current through tube I will drive themotor in one direction, while the current through tube 2 will drive itinthe reverse direction. The tubes l and 2 have to be controlled in such away 0 that while the motor is supposed to stand still the currentthrough both tubes is equal or zero. If the motor has to run one way,the current in one tube should be larger than in the other one, and, ifit is desired to reverse the motor, the quantity of current through thetubes should be reversed. We show the following means for this controlof the tubes.

l4 and I5 are two equal chokes joined at one end which in turn isconnected to point 9 ofthe secondary of transformer 3. Two thermionicvalves I6 and H are connected in such a way between points I8 and 9 oftransformer 3 that their plate current has to pass through chokes l4 andIS. A filament 'windingz l9 provides heating current for the filamentsof tubes l6 and ll and has its center tap connected to point l8 of thesecondary 1 through potentiometer 20, the slide of which takes off thenecessary grid bias for tubes IG'and II. The grids of tubes I6 40 and Ilare controlled through transformer 2|, the secondary of which is centertapped and connected to the filament of the tubes. The primary of thetransformer 2| is connected to thesecondary of the transformer 22, whichconstitutes the input device. The primary 23 of this transformer isshown connected by dotted lines to the supply lines 5 and 6; it carriesA. C. in phase with the A. C. potential on coil 1. If coil 23 'is turnedaround so that its axis is vertical to that of the winding 22. notransfer of energy will be efiected. If, however, coil 23 is in anyposition but vertical, then A. C. of equal phase relation, but with itsamplitude proportional to the sine ofthe angle between the two axes ofthe y h the:

oils, will be induced in coil 22. It can readily e seen that thepotential induced in 22 will ither be zero or phase or in opposite phaseith that in coil 23. In other words, if the vercal position between thetwo axes is taken as the balance or zero point, turning coil 23clockwise will produce a potential in phase with I, while'turningcounter-clockwise will produce a potential of opposite phase.

Suppose iatthe axis of 23 and 22 is parallel at one given moment in suchrelation that the is in phase with that of the supply. us transformer25, in its secondary, will a C. potential which will make the l to be ofopposite potential comwith that of tube i because the center of the coilis connected to the filaments. sstime that the in tube ll is positive,tube will pass a comparatively large plate "'nt, while tube i6, due toits negative grid, pass a comparatively small plate current. "zese platecircuits naturally will only pass current during the positive half-cycleof the 3. potential generated in winding 1. If 'we tuil'l coil throughan arc of 180, we thereby reverse the grid potentials on tubes 15 and H.Tube "i will now have a negative. grid, while that of tube 56 ispositive. Therefore, tube ll now passes a small plate current and tube16 passes a high plate current. These plate currents pass through thechokes H and [5. It is a well known fact that by passing current througha choke the phase relation 01 the A. C. network is changed. In our case,one end of choke i4 is connected to the grid of rectifier tube 2 and thecorresponding end of choke I5 is connected to the grid of rectifier tubel. Both filaments are connected to the center point 8 of winding 1,while the current through the chokes passes from point 9 through thechokes, through the tubes to point I8. point 24 and point 8, which isnothing else but the grid potential on grid 2, is always equal to thepotential between 8 and 9, or 8 and I8. It will be in phase with 8-9 ifthere is no current passing through choke l4 and it will be in. phasewith 8-48 if the internal resistance of tube I6 is zero. It is obviousthat by selecting the proper kind of tubes, or, instead of tubes, resistance, it is possible to swing the vector of the potential between 8and 24 through the full 180 from 8--9 to 8-48.

Due to the properties of the grid glow tubes, the output current of suchtubes can: be controlled by such a change of phase of the grid voltage.Once the grid voltage gets positive enough to allow the plate current tostart, it will continue to pass current until the plate voltage hascompleted its present positive halfcycle. By shifting the phase of thegrid voltage, one can select the time during the positive halfcycle atwhich the plate current will start to flow. If the grid volt-age is inphase opposition to the plate voltage, the tube cannot pass any current,as during the full half-cycle the grid voltage will be negative. Assoon, however, as the grid voltage is shifted slightly to a. laggingposition, the, current will start during the last fraction of thepositive half-cycle. In other words, the average plate current will bevery small. By making the grid voltage vector lag more, and more, onecan gradually and continuously change the average plate current fromzero to its maximum.

""30 action of the tubes 18 and IT in this in- The potential betweenvention is such as to change the phases of the grid voltage vectors withrespect to the plate voltage vectors by allowing more or less current toflow through the chokes l4 and I5 as they are active during the samehalf-cycle as the rectifiers. The more current flows, the more will thegrid vector be in opposition to the phase vector and tend to stop thecurrent flow through the rectifiers. If coil 23' is in the zeroposition, the plate currents through tubes I6 and H and also thecurrents through chokes H and are equal. At this point, therefore, theoutput current of the rectifier tubes is also equal. The value of thiscurrent can be regulated within wide limits by selecting the'workingpoint on the characteristic of the vacuum tubes [6 and I1. Preferably,the vacuum tubes are operated with a very small negative grid bias so asto make the initial plate current rather high. Thereby, the grid'vectcrof the rectifier tubes is moved to a point nearly in opposition to theplate vector and the output current is small.

As soon as coil 23 is moved out of its zero position to one side, theplate or choke current in one branch will be higher, while the similarcurrent in the other branch will be smaller than before. Thereby, thegrid vector of one rectifier is moved to a position more lagging, whilethe corresponding vector of the other rectifier is moved to a lesslagging position. One rectifier, therefore, will pass more current thanthe other one with the result that the motor will run in the desireddirection. In order to reverse the motor, it is necessary to move coil23 back through the zero point to the other side, thereby shifting thephases of the grid voltages of the rectifier tubes in the opposite sensethan before, which results in a reversal of the motor.

While this circuit will control the motor with excellent results as longas it is heavily loaded and enough friction is present to prevent themotor from hunting in its zero position, it is not sufllcient forpositive motor control in all such cases where the motor is employed ina follow-up system. To make a follow-up system out of the circuit shownin Fig. 1, it is only necessary to provide a. direct or gearedconnection between the shaft of the armature H of the power motor andthe pivot point of coil 22, which might be mounted so that itcan beturned around an axis vertical to the axisof the coil. Also, coil 23might be pivoted on another axis in line with that of the pivot of coil22. Coil 23 might be located on the sensitive element of a gyro compass.or other compass, or on the pivot of a delicate measuring instrument,the motions of which have to be followed and translated into power. Ifthe coils are in their respective zero positions, which means that coil23 is standing still and coil 22 has reached a position in which thecoil axis is vertical to that of 23, the inertia of the gears and themotor armature will make the motor hunt around the zero position, u suchsensitive arrangements cannot tolerate any friction on the motor-drivenparts. The only way to make the motor stop at the point is to make bothrectifier tubes stop entirely at thatpoint, which means that their gridvectors would have to be in full opposition to the plate vector.However, such an arrangement has grave disadvantages. It is necessary toselect a. working point on the vacuum tubes I6 and I! near the break ofthe curve in order to get enough current through the same to stop therectifier-s. This means that in order to reduce the initial l in muchthe same way as in Fig. l.

' resistor 51.

plate current sumciently to make the tubes start, an appreciable angleof motion would have to take place on coil 23 before this can beaccomplished. It, therefore, is obvious'that there will be quite a widedead spot" through which the coil 23 can move without the motor llmaking the coil 22 follow coil 23. If coil 23 should be in continuousmotion, this dead spot will mean that coil 22 will follow coil 23 with.an appreciable lag.

Our present invention has successfully overcome this disadvantage bymaking both rectifier tubes pass an appreciable percentage of theirmaximum current in the zero position and by preventing the motor frombreaking into a hunt. It will be obvious that in such a case thedifferential action between the two plate currents of the rectifierswill provide a very sharp zero point and a v'ery small lag on following.

Fig. 2 shows a system of the general character as Fig. 1, in which thishas been accomplished. Rectifier tubes I and 2 are placed. in thecircuit They feed the motor field coils I2 and i3 through. the armatureH and a seriesresistancc 3i, while their grid voltage vector iscontrolled by the chokes l4 and I; An additional choke 34 is providedtogether with a condenser 35 across the choke, the choke being in serieswith the two chokes l4 and I5 respectively. The vacuum tubes l6 andthrough the chokes 34, I4 and i", and their filaments, through the midtap of heating coil 38, are connected-to point 39 of the winding 40 oftransformer 4|. In series with this connection. is the potentiometer 42which allows the adjustment of the grid bias for tubes i5 and I]. Theplate potential for these tubes is supplied between points 39 and 43 ofwinding 4ll, while the wind'ng between 43 and 44 provides plate supplyfor the rectifier tubes.

The input device is shown in the same schematic way as in Fig. 1,consisting of an adjusta'ble transformer 22, the secondary of which isconnected to one half of the primary of transformer 46. It is shownconnected between points 41 and 48, the latter being the mid tap ofthat. winding. The secondary 49 of transformer 46 splits the signal upin its usual way and gives the grids of tubes l6 and I1 oppositepotentials. So far, thiscircuit is very much the same as in Fig. l withthe exception of choke 34 which serves the purpose cf fixing. thestarting point slider.54 across the potentiometer 55 permits a i changein the relative value of grid and plate voltage for tube 50. Atransformer 54 has one winding in the plate circuit of tube 50 andanother winding in its grid circuit, this winding being paralleled byresistor 51 and condenser 58.

This arrangement makes tube 50 a self-starting oscillator of which thefrequency can beadjusted by changing the value of condenser 58 and theamplitude of whichcan be adjusted by changing get through to transformer46.

i1 receive their piste current follow-up system exceptionally stable.

plate circuit of tube 50 which also includes potentiometer 58. By movingthe slider across this potentiometer, the amplitude of the oscillationsgetting into the primary of transformer '46 can be controlled. In otherwords, if the slider is moved to the right, the oscillations willbe attheir maximum, while if it is moved to the left they will approach zero,or no oscillations will The oscillations, which preferably are selectedaround a frequency of between to 60 per second, will be transmitted tothe grid of ,the vacuum tubes, and these tubes will oscillate at thesame frequency. The oscillations produce periodic changes on the platecurrents of these tubes in such a way that while the plate currentthrough one tube is swinging up the current through the other one swingsdown. It is obvious that these oscillations will periodically change thecurrent through the chokes l4 and I5 and thereby make the grid voltagevectors for the rectifiers vibrate around their zero position in such a.way that while one swings to a more lagging position the other oneswings to a less lagging position. The result is that the outputcurrents of the rectifier tubes are periodically changing at the samefrequency, which causes the armature H of the motor to oscillate backand forth at the same predetermined frequency.

If we again assume that the motor is connected to the input transformer22 in such a way as to constitute a. follow-up system, the oscillationsof the motor will be mechanically transmitted to the transformer 22,which in turn will transmit the mechanical vibrations in form ofelectrical fluctuations back into the circuit where the same processstarts all over again. Once the oscillation is started, it takes only afraction of a second to reach its minimum at which it will staycontinuouslyp It must be understood, however, that these oscillations inno way interfere with the normal signal trans mitted through the inputdevice 22. If a misalignment between the coils occurs, it will cause themotor to follow the other coil in just the same way as if nooscillations were introduced into the motor. The main feature of theoscillations, however, is that they interrupt the plate current flowoften enough to prevent the building up of a hunting action on themotor. This continuous and periodic interruption will also prevent anysudden surges of current through the motor and thereby will make theExperience has shown that an oscillating rectifier controlled motor willfollow its controlling element within very close limits, which, in mostcases, are conslderaby below one minute of arc.

Fig. 3 shows the same general arrangement r as Fig. l and Fig. 2 withthe exception that the input system shown is that of a follow-up controltransformer, as shown in our previous application, now Patent #1359304,dated May 22, 1934. The three-legged transformer core 60 is mounted onthe follow-up element which is driven directly or by gears from theshaft of the armature H, of the power motor. The control armature SI ofthe transformer core 60 is mounted on the sensitive element, the motionsof which have to be reproduced by the follow-up system. 62 is theprimary of this transformer which is supplied with A. C. from the A. C.-mains Sand 6. The secondaries 65 and 66,

The oscillations pass through the which are tuned to the particularfrequency of 3 supply system, are arranged and connected such'a thattheir respective potentials are equal and in the zero point. If thearmature 5i moves off towards one side, the potential of one coil willprevail; if it moves to the ot. er side, the potential of the ot r soilwill prevail. There-- fore, the output of this deice would have the samecharacteristics as those shown as 22 in Figs. 1 and 2. The inputtransformer 45 and the arrangement of the vacuum tubes as well as thechokes and the grid glow tubes, together with the motor, are identicalto tho e shown before. The only clir'ierence the oscillator tube v. chis here shown as an A. C. supplied oscille. or. Its plate voltage isprovided between the points and 5!? of the transformer T0. grid bias isprovided by the potentiometer which is connected between the mid pointof the heater winding I2 and point '69 of transformer iii. Theperformance of this circuit is identical to that shown in Fig. 2.

shows an improved circuit in which the oscillator tube has beeneliminated. We provide a special transformer I3 which is connected withone winding across the two field coils l2 and 53 of the motor II. Thecondensers TI and '58,.which are also shown in the preceding figures andwhich are provided to minimize the effect of self-induction of the coilsI2 and I3 also tune the winding I9 of transformer I3, each half of thewinding being tuned by one of the condensers. Coil 80 of transformer I3is tuned by condenser BI which is in series with rheostat 82. Thisrheostat serves the purpose of changing phase, frequency and amplitudeof the oscillations which are started in this transformer and make tubesI6 and I1 oscillate. The output of coil 80 is connected to one half ofthe input transformer 83 between points 80 and 85. The signal input isconnected between points 85 and 86. Of further importance are the verysmall condensers 8l' and 88 which are shown connected between the platesand filaments of the vacuum tubes I8 and I1. These condensers at thesame time connect the grids of the rectifiers I and 2. There are severalpossible explanations for the action of these condensers. The mostplausible one seems to be that they provide a path of A. C. through thechokes while the vacuum tubes I6 and I1 have negative plate voltage andare inactive. In other words, these condensers allow a more continuousflow of A. C. through the chokes instead of only rectified A. C. like inthe other circuits shown. Of further importance is the size of thecondenser 83 across choke coil 94 which is in series with the controlchokes. Changing this condenser results in a change of frequency of theoscillations set up in the system by means of transformer I3.

It is possible to arrest the motor shaft so that the same cannot move atall and still the cur-- rent surges of the electrical oscillations willcontinue to tug at the motor, which can be proved by measuringinstruments in the motor leads. In other words, what is set up in thecircuit is an electrical oscillation and its effect on the motor is notto be confused with a fast hunt. A hunt, no matter how fast, can alwaysbe stopped mechanically by stopping the motor. An electricaloscillation, resulting in a mechanical v1- bration of the motor, cannotbe stopped at all, except by opening certain connections in the circuit.The transformer I3 has another very important function. It prevents anyhunting of opposition to each other on the motor even if theoscillations are made extremely small and of high frequency. As soon asthe oscillations become small enough they will have very little effecton surges through the motor or on the inertia of the system. However,the reverse feed back action of transformer I3 will prevent the buildingup of a hunting action at the beginning. For small signals, thetransformer 13 is acting strong enough against the tendency to hunt toovercome the same completely. On strong signals, however, the normalfeed back action in the circuit prevails, resulting in very high torqueof the motor for very small misalignment of the control system. Nospecial input system is shown in Fig. 4 as it is obvious that any ofthose shown in ,Figs 1, 2 and 3 can be used with equal results.

Fig. 5 shows a circuit which is radically different in the way therectifiers are controlled, but which has the some feature of aself-generated oscillation within the system to prevent hunting actionand to increase accuracy. The rectifiers 95, 95, 9'! and 98 are here notcontrolled. progressively by shifting the phase of the grid voltage butsuddenly by changing the magnitude of the grid voltage. It is,therefore, obvious that it is only possible to make the tubes go full onor full off, but that no intermediate position can be secured. Right onthe face of this it will be clear that such a system must of necessitybe a hunting system on account of the violent surges of current everytime a tube is started. The rectifiers are here employed in full waverectifying circuits so that the current supplied to the motor is for allpractical purposes pure D. C. The circuit, however, will work just aswell with two tubes instead of four if the tubes are employed in halfwave circuits. This is likewise true for the preceding circuits in whichfull wave arrangements could be used instead of half-wave by employingtwo tubes on opposite ends of a transformer winding and controllingtheir grid voltage through a transformer, which would make the gridvectors of each pair of rectifiers opposite.

In Fig. 5 transformer 99 has three secondary windings I00, IOI and I02.vides filament energy for the rectifiers; winding IOI is a center tappedplate supply winding for rectifiers 95 and 96; while I02 is a similarwind- Ing for rectifiers 91 and 98. The output current of the rectifiersgoes from the center tsp of winding I through the motor armature II andthen through the motor field coils I2 and I3 back to the center taps ofwindings IN and I02, respectively, and from there through the tubes tothe filaments. The control for the grid voltage of these taps isachieved by means of two vacuum tubes I and I06, which in turn arecontrolled from a conventional input system I01 which acts in identicalway as explained before. The plate supply for the tubes I05 and I06 issecured from transformer I00, which has a secondary winding I09 tosupply filament energy to the tubes and two separate plate supplywindings H0 and III. One of each of the windings H0 and III is connectedto one each of the plates of the tubes I05 and I00. Between the otherends of the two windings is connected 9. center tapped resistor H2, thecenter tap of which is connected to the filament of the-rectifier tubes.It is obvious that a signal will affect both grids of the tubes I05 andI06 equally, while their plates are of opposite potential. This meansthat these tubes act in a push-pull fashion Winding I00 proimpulse ofcurrent caused by the full on or off The plate currents of the tubeshave to pass through one half each of the resistor I I2. The condensersH3 and Ill are connected across the resistor II2 so that the rectifiedA. C. voltage drop across each half of the resistors is filtered to suchan extent that it is D. C. for practical purposes. As will be seen inthe diagram, the free ends of the resistor are connected to the grids ofeach pair of rectifier tubes respectively. Therefore, if a voltage dropin one half of the resistor occurs, it will change the grid voltagelevel on the respective pair of rectifiers. Inasmuch as the vacuum tubesI05 and I06 work in opposition to each other, the rectifiers are alsocontrolled in opposition, which means that while one pair of tubespasses current the other pair of tubes is inactive, thereby making themotor respond to whatever inputsignal is introduced.- As said before,this arrangement will make the motor hunt because of the sudden controlof the rectifier-s.

In order to suppress the hunting action, we

, provide a transformer H5 which acts as hunt suppressorand which alsomakes the vacuum tubes oscillate in a similar way as explained in Fig.4. The winding H6 of the transformer is center tapped, the center tapbeing connected to the input transformer I01. To the ends of the windingIII; we connect the grids of tubes 505 and I06. The other winding II! isconnected through'condensers H8 and H9 to the ends of the resistor II2.It is obvious that any voltage drop across the resistor II! will cause acorresponding voltage drop across the coil H1. The A. C. component ofthis voltage drop will be transmitted to the grids of the tubes I05 andI06. It is seen, therefore, that the tubes will oscillate as one coil ofthe transformer is in the grid circuits while the other one is in theplate circuits. The tuning is accomplished by condenser I20 which isacross winding H6, while the amplitude of the oscillation is limited bythe parallel resistor IN. The oscillations cause periodic voltage dropsacross resistor I I2 thereby changing the grid potentials on the gasfilled tubes at the same frequency, which in turn results in a similaroscillation of the motor shaft. If a signal is transmitted through theinput device, these oscillations will have a higher amplitude in onepair of rectiflers than in the other pair, and the motor will follow thesignal just as if the oscillations were not present at all. The huntsuppressing action is similar to that explained for Fig. 4. To a certainextent the oscillations themselves will prevent the hunt by interruptingthe continuous flow of current through the motor in just the same way asshown in Fig. 2 where there was no hunt-suppressing device but onlyanosciilator.

By our system we control a reversing motor by means of grid controlledrectifiers in such a way that the normal tendency of the motor to huntis prevented by either oscillations or a huntsuppressing device or byboth. The greatest advantage of such an arrangement is that there willbe no dead spot if the circuit is'used for a follow-up system. Theincrease in accuracy is quite large and enables the follow-up system towork with very small lag without sacrificing either torque orsensitivity.

Furthermore, the introduction of oscillations right into the motorprovidesan excellent means of keeping all mechanical parts in continuousmotion, thereby eliminating any static friction.

In other words, it is not necessary to provide an excessive amount ofpower to break the parts loose to start-them. They are in a continuouslystarting condition at all times.

Ifhe combination of the just mentioned features makes our system verywell adapted to such apparatus where extreme accuracy has to be coupledwith high torque and sensitivity.

In accordance with the provisions of the patent statutes, we have hereindescribed the principle and operation of our invention, together withthe apparatus which we now consider to represent the best embodimentthereof, but we,

desire to have it understood that the apparatus shown is onlyillustrative and that the invention can be .carried out by other means.Also, while it is designed to use the various features and elements inthe combination and relations described, some of these may be alteredand others omitted without interfering with the more general resultsoutlined, and the invention extends to such use.

Having described our invention, what we claim and desire to secure byLetters Patent is:

1. In a remote control for power motors, the combination with areversible commutator motor, of a pair of grid-glow tubes having theirplates connected to drive the motor in opposite directions, atransformer controller, a pair of vacuum tubes controlled by saidcontroller, an inductance in circuit with each vacuum tube, eachgrid-glow tube having its grid connected to a point between eachvacuumtube and its inductance, and a common A. C. supply for all said tubesand said controller whereby changes in the position of the controllergoverns the direction and torque of the motor by shifting:

- the phase of the grid voltage with respect to that of the plate of theglow tubes.

2. In a. remote control for power motors, the combination with areversible commutator motor, of a pair of grid-glow tubes having theirplates connected to drive the motor in opposite directions, atransformer controller, a pair of vacuum tubes, controlled by saidcontroller, an inductance in circuit with each vacuum tube, eachgrid-glow tube having its grid connected to a point between each vacuumtube and its inductance, a common A. C. supply for all'said tubes andsaid controller, and an oscillator in said circuit for preventinghunting of the motor without producing a dead region.

3. In a positional or follow-up control system for power motors forpositioning an object with respect to the position of a controllingobject, the combination with the controlling object and.

a controlled object driven therefrom, of means for producing anelectro-motive force varying in magnitude and direction with theposition of said controlled object, a pair of grid-glow tubes,phase-shifting devices between said means and said glow tubes variablewith the output of said means, an A. C. supply for said tubes, areversible motor for driving said controlled object and governed as todirection and torque by the output of said grid-glow tubes, and anoscillator in said system for preventing hunting of said motor withoutproducing a dead region.

4. In a positional or follow-up control for power motors for positioningan object with respect to the position of a controlling object, thecombination with the controlling object and a controlled object driventherefrom, ofmeans for producing an electro-motive force varying inmagnitude and direction with the position of said controlled object, agrid-glow tube unit, the output 01 which is governed from said means, areversible power motor for driving said controlled object and controlledas to movement and torque from said out at, and an oscillator forrapidly and alternate y interrupting the plate current flow through saidunit to prevent a hunt from building up by causing a rapid smallamplitude tremor.

5. In a positional or iolloiv-up control for power motors forpositioning object with respect to the position or a controlling object,the combination with the controlling object and a controlled objectdriven therefrom, of means for producing an electro-motive force varyingin magnitude and direction with the position of said controlled object,a reversible motor for driving the controlled object, and means forcausing said motor to follow the movements of the controlling objectwithin close limits without appreciable hunting including a grid-glowtube unit and means of causing the same to continuously and oppositelyoscillate.

6. In a follow-up system for sensitive instruments, the combination witha sensitive and a following element, of a grid-glow tube relayamplifying system, means controlled by relative movement of thesensitive and follow-up elements for governing the input to said system,a motor governed by the output of said system for driving said followingelement, and a feed back means in said system for preventing mechanicalhunting of the said motor.

7. In a follow-up system for sensitive instruments, the combination witha sensitive and a following element, of a grid-glow tube relayamplifying system, means controlled by relative movement of thesensitive and follow-up elements for governing the input to said system,a motor governed by the output of said system for driving said followingelement, a normal feedback means, and an auxiliary feed-back transformer for opposing the building up of huntproducing surges.

8. In an electrical follow-up system, a twopart controller mounted onthe sensitive and follow-up elements wherein relative movement betweensuch parts in one direction or the other creates an output of oppositephase, a grid-glow tube system controlled by such output, a motorcontrolled from the output of said system, and means for setting up insaid system an oscillatlon of the proper frequency to set up tremors ofsmall amplitude in said motor and followup system.

9. In a remote control system for reversible motors, an alternatingcurrent supply, a controller excited therefrom, a grid-glow tubeamplifying system connected thereto, a multi-wound transformer poweredfrom said supply for supplying filament, plate and grid potentialsthereto, a motor connected to the output of said system, and anoscillatory transformer connected between the output of the system andthe input to maintain an electrical oscillation and oppose hunting ofsaid motor.

10. In a re to control system for reversible motors, an al ting currentsupply, a. controller excited therefrom, a grid-glow tube amplifyingsystem connected thereto, a multi-wound trans former powered from saidsupply for supplying filament, plate and grid potentials thereto, a.motor connected to the output of saldsystem, said circuit having feedback characteristics, a; feed back or buckingtransfonner and condensersconnected in the output of the system, and means for tuning thetransformer condenser circuit to produce electrical oscillations in saidtubes and motor.

11. In a remote control system for reversible motors, the combinationwith the motor, of an alternating current supply, a controller excitedtherefrom, a grid-glow tube amplifying system connected thereto, amulti-wound transformer powered from said supply for supplying filament,plate and grid potentials thereto, a pair of windings controlling thedirection of said motor, a multi-wound transformer having one part ofits primary across one of said windings and another part across theother winding, a condenser across each part, the secondary windinghaving a feed back connection to the input, a condenser and variableresistor across said secondary, said motor being controlled by theoutput of said system.

12. In a remote control for power motors, the combination with themotor, of a pair of grid glow tubes having their plates connected todrive the motor in opposite directions, a transformer controller, a pairof vacuum tubes and inductances controlled by said controller and havingtheir output connected to the respective gridglow tubes, a condenserbetween the plate and filament of each tube, a pair of windingscontrolling the direction of said motor, a multiwound transformer havingone part of its primary across one of said wlndingsand another partacross the motor winding, a condenser across each part, the secondarywinding having a feed back connection to the input, and a condenser andvariable resistor across said secondary.

13. In a remote control for power motors, the combination with a doublewound motor, of a pair of grid-glow tubes having their plates connectedto drive the motor in opposite directions, a transformer controller, apair of vacuum tubes and inductances controlled by said controller andhaving their output connected to the respective grid-glow tubes, 2.third inductance shunted by 'a condenser in circuit with the common ofsaid other lnductances and the plate supply of the vacuum tubes, amultl-wound transformer having one part of its primary across one motorwinding and another part across the other motor winding, a condenseracross each part, the secondary winding having a feed back connection tothe input, and a condenser and variable resistor across said secondary.

14. Means for substantially eliminating mechanical hunt and lag inreversible power driven "follow-up systems employing an electron tubeamplifier for the control of the output of a gridglow tube rectifier,comprising a plurality of feedback circuits, at least one of whichincludes means to produce adjustable electrical oscillatlons andhunt-opposing characteristics in the electron tube amplifier, therebyperiodically starting and stopping the output of said glow tuberectifier in opposition at the frequency of said oscillations and meansfor reproducing these electrical oscillations as mechanical oscillationsin the power motor.

15. Means for substantially eliminating static friction, mechanical huntand lag in a reversible power driven follow-up system employing analternating current power supplyand vacuum tube amplifier system forcontrolling the output of a grid-glow tube system driving the reversiblemotor, comprising means for creating within said system and means forsuperimposing on the supply and signal frequency an oscillation of a,frequency low enough to produce in the motor armature a mechanicaloscillation of relatively small amplitude.

16. In a positional or follow-up control for power motors forpositioning an object with respect to the position of a controllingobject, the combination with an A. C. supply, a controller energizedtherefrom and adapted to produce a signal which varies in magnitude anddirection as the position of the controlled and controlling objectchanges, a pair of oppositely connected electron tubes governed by saidcontroller, an inductance in circuit with each tube, a midtappedtransformer connected across said tubes and inductances, a pair ofgrid-glow tubes, each having its filament connected to the center tapof' said transformer and its grid to a point between one of saidelectron tubes and its inductance, and a reversible commutator motorconnected to the plates of said glow-tubes whereby its torque anddirection are governed by the relative position of the controlling andcontrolled elements.

BRUNO A. WITTKUHNS.

FREDERIC M. WATKINS.

